As is known, locks for motor vehicles generally comprise a supporting body designed to be fixed to a door of the motor vehicle, and a closing mechanism carried by the supporting body and designed to couple with a lock striker fixed to an upright of the frame of the door itself. There exist moreover solutions, used much more rarely, in which the supporting body of the lock is constrained to the upright, and the lock striker is instead fixed to the door.
In both cases, the closing mechanism is formed basically by a fork and a dog or catch hinged to the supporting body about respective fixed axes parallel to one another.
The fork has an engagement seat for a generally cylindrical portion of the aforesaid lock striker, is elastically loaded towards an opening position, in which it enables engagement and disengagement between the lock striker and its seat, and can assume a closing position, in which it withholds the cylindrical portion of the lock striker within its seat and prevents disengagement thereof.
The dog is pushed by a spring to couple via snap-action, by means of an engagement edge thereof, with a peripheral retention shoulder of the fork for blocking the latter in a releasable way in the closing position.
In particular, following upon slamming of the door, the fork is displaced, under the thrust of the lock striker, from the opening position to an overtravel position set beyond the closing position; during the stretch of travel comprised between the closing position and the overtravel position, the fork passes, with its own retention shoulder, beyond the dog, enabling the latter to snap, with its own engagement edge, into a position facing the aforesaid shoulder. During the subsequent elastic return of the fork towards the opening position, the retention shoulder sets itself bearing upon the engagement edge of the dog, which thus defines the closing position of the fork itself on the lock striker.
In the case of presence of dirt or formation of ice inside the lock, the dog may be slowed down in its movement towards the position of coupling with the fork so that, as the door comes close to the corresponding frame, closing does not occur, with a consequent bouncing back of the door itself.